Dielectric filter with protective film covering the edges of the input/output electrodes and external electrode

ABSTRACT

The invention relates to a dielectric filter for mounting to a printed wiring board wherein the edges of the filter&#39;s electrodes are covered with a protective film to prevent the peeling of edges of electrodes. The dielectric filter is a dielectrics (1) having a through hole (2) extending from its top to bottom face, an external electrode (3a) disposed on the outer face of the dielectrics (1) except for the top face, an internal electrode (3b) disposed inside the through-hole (2), island-like input/output electrodes (6) which are disposed on the outer side face of said dielectrics (1) and surrounded by a non-electrode portion (5) of the external electrode (3a). An electrode protection film (8) covers an outer edge of said input/output electrode (6), the non-electrode portion (5) of the external electrode (3a) disposed around the input/output electrode (6), and an inner edge of the external electrode (3a) contacting the non-electrode portion (5).

BACKGROUND OF THE INVENTION

The present invention relates to a dielectric filter used incommunications equipment and a method of manufacturing the dielectricfilter. Also, the present invention relates to a protection film forcovering the edges of the filter's electrodes

Conventionally, dielectric filters have an island-like input/outputelectrode, isolated from an external electrode, disposed on the outerside face of dielectrics having multiple through holes from the top tobottom.

One problem faced with a conventional dielectric filter is the peelingof the outer edge of the input/output electrodes and the inner edge ofthe external electrode of the dielectric filter, which may occur due toexternal stress, such as heat and twist applied to printed wiring boardswhen the dielectric filters are mounted to the printed wiring boards.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is to prevent the peeling of theedges of electrodes of a dielectric filter.

In order to achieve this object, the present invention relates to adielectric filter comprising, dielectrics having a through holeextending from its top to bottom face, or non-through hole, an externalelectrode disposed on the outer face of the dielectrics except for thetop face, an internal electrode disposed inside the through hole ornon-through hole and island-like input/output electrodes, which aredisposed on the outer side face of the dielectrics and surrounded by anon-electrode portion of the external electrode. An electrode protectionfilm covers the outer edge of the input/output electrode, thenon-electrode portion of the external electrode around the input/outputelectrode, and the inner edge of the external electrode contacting thenon-electrode portion.

With the above structure, the present invention prevents the peeling ofthe outer edge of the input/output electrode and the inner edge of theouter electrode, which may occur due to external stress, such as whenheat is applied thereto. The protective film covers the outer edge ofthe input/output electrodes and the inner edge of the outer electrode ofthe dielectric filter.

The invention itself, together with further objects and attendantadvantages, will best be understood by reference to the followingdetailed description taken in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a perspective of a dielectric filter of a preferred embodimentof the present invention.

FIG. 2 is a sectional view of an input/output electrode of thedielectric filter of FIG. 1 depicting a state of application of anelectrode protection film.

FIG. 3 is a plan view of an input/output electrode of the dielectricfilter of FIG. 1.

FIG. 4 is an exploded perspective view depicting the mounting of apreferred embodiment of a dielectric filter on a printed wiring board.

FIG. 5 is a front section view of the dielectric filter of FIG. 4 of thepresent invention mounted to a printed wiring board.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of a dielectric filter of the present inventionis described below with reference to the drawings.

FIG. 1 is rectangular dielectrics, or dielectric material, 1 made ofBaTiO₃ -system ceramic. The dielectric material 1 has three cylindricalthrough holes, or non-through holes 2 extending from a top face (theopen end) to a bottom face (the short-circuit end), an Ag-systemexternal electrode 3a encasing the dielectrics on the outer side facesand bottom face of the dielectric material, an Ag-system internalelectrode 3b on the internal face of each of the through holes 2, andcapacity forming electrodes 4. Each capacity forming electrode 4 isconnected to an internal electrode 3b, on the top face or open end.

A pair of C-shaped non-electrode portions 5 are disposed in a portion ofexternal electrode 3a formed on an outer side face, at the open end, ofthe dielectric material 1. An island-like input/output electrode 6 isformed inside each of the C-shaped non-electrode portions 5, facing thethrough holes 2. An electrode protection film 8 is provided to cover theouter edge of the input/output electrode 6 and the inner edge of thecut-away portions of the external electrode 3a formed on the outer sideface.

FIG. 3 shows in greater detail how the corners 7 of the edge of theinput/output electrode 6 and the edge of the external electrode 3a arecurved to prevent a concentration of stress on the corners 7. Theelectrode protection film 8 is provided to cover the outer edge of theinput/output electrode 6, the non-electrode portion 5, and the inneredge of the external electrode 3a. Thus, with the provision of theelectrode protection film 8, the edges of the input/output electrode 6and the external electrode 3a, which would otherwise be subject topeeling, can be protected.

The electrode protection film 8 is formed by applying a glass pastemixture of glass-ceramic and amorphous glass. One of the advantages ofamorphous glass is its high strength. However, amorphous glass is likelyto remelt under high temperature. This disadvantage of amorphous glasscan be counteracted by fixing amorphous glass with glass-ceramic, whichhas good temperature characteristics.

Furthermore, as shown in FIG. 2, the outer end face 9 of theinput/output electrode 6 and the inner edges 10 of the externalelectrode 3a are curved. If the outer end face 9 and inner edges 10 wereto have sharp edges, the electrode protection film 8 applied to suchedges would become thinner and the effect of the electrode protectionwould be degraded. Edges of such end faces are rounded off to prevent adegrading in the effectiveness of the protective film 8.

A method of manufacturing the dielectric filter according to the presentinvention is described below.

First, in forming the external electrode 3a and the input/outputelectrodes 6, silver paste is applied to the dielectrics 1, on the facewhere the electrode protection film 8 will be formed, by means such asscreen printing. The edges of the printed silver paste (the outer endface 9 and the inner edges 10) are sharp at this point. The silver pasteis then heated up to approximately 850° C. to form the electrodes en thedielectrics 1. The silver paste melts and the edges of the electrodesbecome curved during the heat treatment. Then, after sintering, thefinished end faces 9 and inner edges 10 become rounded, as shown in FIG.2.

Next, glass paste is printed to cover the outer end face of theinput/output electrode 6, the non-electrode portion 5, and the inner endface of the external electrode 3a. Printed glass paste is sintered underthe same heating conditions as those for the silver paste describedabove.

During this process, the input/output electrode 6 and the externalelectrode 3a under the glass paste remelts. This allows the input/outputelectrode 6 and the external electrode 3a to mix with the glass paste.Consequently, the bonding strength between the input/output electrode 6and the electrode protection film 8, and between the external electrode3a and the electrode protection film 8, is strengthened.

Moreover, the silver paste contains a glass component for bonding thedielectric material 1 and the electrodes 6 and 3a. A part of the glasscomponent, which is contained in the edges of the input/outputelectrodes 6 and external electrode 3a, combines with the glass pasteduring remelting, and further improves bonding strength.

FIG. 4 and FIG. 5 illustrate a product of the present invention with thedielectric filter mounted on a printed wiring board 11. Conductivepaste, such as solder paste 13, is applied to the area of theinput/output electrodes 6 and external electrode 3a, and heated topermit the solder to flow. As a result, a product is formed wherein adielectric filter 12 is mounted on a printed wiring board 11.

In particular, the printed wiring board 11 is formed by providing acopper electrode 15 on the surface of an epoxy substrate 14. Contactelectrodes 17 are formed by a method such as etching the copper, therebyexposing non-conductive portions 16.

To form the product, solder paste 13 is applied to the contactelectrodes 17 and a mounting area 18, which is the approximate size ofthe outer side face forming a portion of the external electrode 3a.Then, the dielectric filter 12 is placed over a portion of the contactelectrodes 17 and the mounting area 18, and the input/output electrodes6 are connected to the contact electrodes 17, respectively. Heat isapplied to permit the solder to flow and bond the dielectric filter 12to the printed wiring board 11.

FIG. 5 is an end view looking at the open face of the dielectric filter12 and a cross-section of the printed wiring board 11. Depicted in FIG.5, are the input/output electrodes 6 and the electrode protection film 8of the dielectric filter 12. Also, FIG. 5 shows the contact electrodes17 of the printed wiring board 11.

An area of the input/output electrodes 6 is larger than that of thecontact electrodes 17. This is because, as mentioned previously, theelectrode protection film 8 is formed on the outer edge of theinput/output electrode 6. The area of an input/output electrode 6 isenlarged for the portion covered with the electrode protection film 8.

FIG. 5 also illustrates that the electrode protection film 8 covers boththe outer edge of the input/output electrodes 6 and the inner edge ofthe external electrode 3a. Consequently, as also shown in FIG. 2, a dent18 is formed between the input/output electrodes 6 and the externalelectrode 3a. This dent provides an intentional space 20 between theprinted wiring board 11 and the electrode protection film 8 so as toprevent short-circuiting of an adjacent input/output electrode 6 with anexternal electrode 3a by spreading of the solder paste 13 between theprinted wiring board 11 and electrode protection film 8 due to capillaryaction.

According to the present invention, the electrode protection filmcovering the outer edge of the input/output electrodes and the inneredge of the external electrode on an outer area of the dielectric filterprevents the peeling of the outer edge of the input/output electrode andinner edge of the external electrode, which peeling may otherwise occurdue to external stress, such as heat.

Of course, it should be understood that a wide range of changes andmodifications can be made to the preferred embodiment described aboveand that the foregoing description be regarded as illustrative ratherthan limiting. It is therefore intended that it is the following claims,including all equivalents, which are intended to define the scope ofthis invention.

What is claimed is:
 1. A dielectric filter comprising:a dielectricmaterial having a top face, a bottom face and a plurality of side faces;at least one through hole extending from the top face to the bottomface; a internal electrode disposed inside each through hole; anexternal electrode disposed on the bottom face and the plurality of sidefaces; at least one island-like input/output electrode disposed on aside face of said dielectric material and surrounded by a non-electrodeportion of the external electrode; and an electrode protection filmcovering an outer edge of each input/output electrode, the non-electrodeportion of the external electrode disposed around the input/outputelectrode, and an inner edge of the external electrode adjacent thenon-electrode portion, wherein said electrode protection film is dentedover said non-electrode portion between the outer edge of theinput/output electrode and the inner edge of the external electrode, andan outer end face of said input/output electrode and an inner end faceof said external electrode disposed facing the outer end face of theinput/output electrode are curved.
 2. The dielectric filter of claim1,wherein at least one corner of an outer periphery of the island-likeinput/output electrode and an inner periphery of the external electrodedisposed on the outside of the input/output electrode are curved.
 3. Thedielectric filter of claim 1,wherein said electrode protection film is aglass paste mixture of at least glass-ceramic and amorphous glass. 4.The dielectric filter of claim 1,wherein said at least one through holeand said at least one island-like input/output electrode comprised ofmultiple through holes and multiple input/output electrodes,respectively, and are provided at specified intervals.
 5. A dielectricfilter comprising:a dielectric material having a top face, a bottom faceand a plurality of side faces, and having at least one non-through holefrom the top face to the bottom face; an internal electrode disposedinside each said non-through hole; an external electrode disposed on thebottom face and the plurality of side faces; at least one island-likeinput/output electrode disposed on a side face of said dielectricmaterial and surrounded by a non-electrode portion of the externalelectrode; and an electrode protection film covering an outer edge ofeach input/output electrode, the non-electrode portion of the externalelectrode disposed around the input/output electrode, and an inner edgeof the external electrode adjacent the non-electrode portion, whereinsaid electrode protection film is dented over said non-electrode portionbetween the outer edge of the input/output electrode and the inner edgeof the external electrode, and an outer end face of said input/outputelectrode and an inner end face of said external electrode disposedfacing the outer end face of the input/output electrode are curved.
 6. Amethod of manufacturing of a dielectric filter comprising:a dielectricmaterial having a top face, a bottom face and a plurality of side faces,and having at least one non-through hole from the top face to the bottomface; an external electrode disposed on the bottom face and theplurality of side faces; an internal electrode disposed inside each saidnon-through hole; at least one island-like input/output electrodedisposed on a side face of said dielectric material and surrounded by anon-electrode portion of the external electrode; and an electrodeprotection film covering an outer edge of each input/output electrode,the non-electrode portion of the external electrode disposed around theinput/output electrode, and an inner edge of the external electrodeadjacent the non-electrode portion, wherein said electrode protectionfilm is dented over said non-electrode portion between the outer edge ofthe input/output electrode and the inner edge of the external electrode,and an outer end face of said input/output electrode and an inner endface of said external electrode disposed facing the outer end face ofthe input/output electrode are curved, said method comprising the stepsof:applying a silver paste to a side face near the top face by means ofscreen printing to form each said island-like input/output electrode,said non-electrode portion of the external electrode and said inner edgeof the external electrode in contact with the non-electrode portion;firing the silver paste to curve the edges of the electrodes at apredetermined temperature; applying a glass paste to said outer edge ofsaid each island-like input/output electrode, and said non-electrodeportion of the external electrode and said inner edge of the externalelectrode adjacent the non-electrode portion; and then firing the glasspaste at approximately said predetermined temperature as that for theelectrodes, so as to provide said electrode protection film over theouter edge of said input/output electrode, the non-electrode portion ofthe external electrode, and the inner edge of the external electrodeadjacent the non-electrode portion.
 7. A combination of a dielectricfilter mounted to a printed wiring board,said combination comprising:aprinted wiring board; and a dielectric filter mounted on a surface ofthe printed wiring board, wherein the dielectric filter includes,adielectric material having a top face, a bottom face and a plurality ofside faces, and having at least one non-through hole from the top faceto the bottom face; an internal electrode disposed inside each saidnon-through hole; an external electrode disposed on the bottom face andthe plurality of side faces; at least one island-like input/outputelectrode disposed on a side face of said dielectric material andsurrounded by a non-electrode portion of the external electrode; and anelectrode protection film covering an outer edge of each input/outputelectrode, the non-electrode portion of the external electrode disposedaround the input/output electrode, and an inner edge of the externalelectrode adjacent the non-electrode portion, wherein an outer end faceof said input/output electrode and an inner end face of said externalelectrode disposed facing the outer end face of the input/outputelectrode are curved, and wherein the printed wiring board includes,asurface provided with at least one contact electrode connected with saidat least one input/output electrode of said dielectric filter, andanother electrode connected with the external electrode of saiddielectric filter, an area of each input/output electrode of thedielectric filter being larger than that of a corresponding contactelectrode.
 8. The combination of claim 7,wherein at least one corner ofan outer periphery of the island-like input/output electrode and aninner periphery of the external electrode disposed on the outside of theinput/output electrode are curved.
 9. The combination of claim 7,whereinsaid electrode protection film is a glass paste mixture of at leastglass-ceramic and amorphous glass.
 10. The combination of claim7,wherein said at least one non-through hole and said at least oneisland-like input/output electrode comprised of multiple non-throughholes, and multiple input/output electrodes, respectively, and areprovided at specified intervals.
 11. The combination of claim 7,whereinsaid electrode protection film is dented over said non-electrode portionbetween the outer edge of the input/output electrode and the inner edgeof the external electrode.
 12. A dielectric device comprising:adielectric material having a top face, a bottom face and a plurality ofside faces; an external electrode disposed on the bottom face and theplurality of side faces; at least one island-like input/output electrodedisposed on a side face of said dielectric material and surrounded by anon-electrode portion of the external electrode; and an electrodeprotection film covering an outer edge of eachinput/output electrode,the non-electrode portion of the external electrode disposed around theinput/output electrode, and an inner edge of the external electrodeadjacent the non-electrode portion, wherein said electrode protectionfilm is dented over said non-electrode portion between the outer edge ofthe input/output electrode and the inner edge of the external electrode,and an outer end face of said input/output electrode and an inner endface of said external electrode disposed facing the outer end face ofthe input/output electrode are curved.
 13. The dielectric device ofclaim 12,wherein said electrode protection film is a glass paste mixtureof at least glass-ceramic and amorphous glass.
 14. The dielectric deviceof claim 12,wherein said electrode protection film is dented over saidnon-electrode portion between the outer edge of the input/outputelectrode and the inner edge of the external electrode.
 15. Thedielectric device of claim 14,wherein said electrode protection film isa glass paste mixture of at least glass-ceramic and amorphous glass. 16.The dielectric device of claim 14,further comprising multiple throughholes and multiple input/output electrodes are provided on saiddielectric material at specified intervals.